Avoid deadlocks by using lambdas for context lock (#2625)

ctx.input().key_pressed(Key::A) -> ctx.input(|i| i.key_pressed(Key::A))

README.md

@@ -371,6 +371,8 @@ egui uses the builder pattern for construction widgets. For instance: `ui.add(La
 
 Instead of using matching `begin/end` style function calls (which can be error prone) egui prefers to use `FnOnce` closures passed to a wrapping function. Lambdas are a bit ugly though, so I'd like to find a nicer solution to this. More discussion of this at <https://github.com/emilk/egui/issues/1004#issuecomment-1001650754>.
 
+egui uses a single `RwLock` for short-time locks on each access of `Context` data. This is to leave implementation simple and transactional and allow users to run their UI logic in parallel. Instead of creating mutex guards, egui uses closures passed to a wrapping function, e.g. `ctx.input(|i| i.key_down(Key::A))`. This is to make it less likely that a user would accidentally double-lock the `Context`, which would lead to a deadlock.
+
 ### Inspiration
 
 The one and only [Dear ImGui](https://github.com/ocornut/imgui) is a great Immediate Mode GUI for C++ which works with many backends. That library revolutionized how I think about GUI code and turned GUI programming from something I hated to do to something I now enjoy.
@@ -396,6 +398,7 @@ Notable contributions by:
 * [@mankinskin](https://github.com/mankinskin): [Context menus](https://github.com/emilk/egui/pull/543).
 * [@t18b219k](https://github.com/t18b219k): [Port glow painter to web](https://github.com/emilk/egui/pull/868).
 * [@danielkeller](https://github.com/danielkeller): [`Context` refactor](https://github.com/emilk/egui/pull/1050).
+* [@MaximOsipenko](https://github.com/MaximOsipenko): [`Context` lock refactor](https://github.com/emilk/egui/pull/2625).
 * And [many more](https://github.com/emilk/egui/graphs/contributors?type=a).
 
 egui is licensed under [MIT](LICENSE-MIT) OR [Apache-2.0](LICENSE-APACHE).